1. Field of the Invention
The present invention relates to a silicon-containing polymer suited as a base resin for a chemically amplified positive resist material used for microfabrication in the manufacture of a semiconductor device and the like; a resist material, particularly chemically amplified positive resist material suited when high energy radiation such as far UV radiation, KrF excimer laser light (248 nm), ArF excimer laser light (193 nm), F2 laser light (157 nm), electron beam and X-ray is used as an exposure light source; and a pattern formation method.
2. Description of the Related Art
With a trend to higher integration and higher operating speeds in LSI devices, the pattern rule has become finer rapidly. Such a rapid progress is attributable to an increase in the NA of a projection lens, improvement in the performance of a resist, and employment of an exposure light having a shorter wavelength. In particular, transition from i-line (365 nm) to shorter wavelength exposure light of KrF laser (248 nm) has brought about a great innovation, making it possible to produce 0.18 μm rule devices. In the trend toward resist materials with a higher resolution and sensitivity, chemically amplified positive resist materials (as described in Japanese Patent Provisional Publication Nos. 02-027660/1990 and 63-027829/1988) using an acid as a catalyst have excellent characteristics so that they become leading resist materials in far UV lithography.
Use of resist materials for KrF excimer laser was started popularly for a 0.3 micron process. After a 0.25 micron rule, a 0.18 micron rule is now adopted for mass production. Moreover, trial manufacture on a 0.15 μm rule is started and even 0.13 μm rule is under investigation. Thus, the pattern rules have become finer in an accelerating pace. Transition from KrF to shorter wavelength ArF (193 nm) is expected to miniaturize the design rule to 0.13 μm or less. Conventionally used novolac resins or polyvinylphenol resins, however, cannot be used as a base resin for resists, because they have very strong absorption in the vicinity of 193 nm. To ensure transparency and necessary dry etching resistance, use of acrylic or alicyclic resins such as cycloolefin have been investigated (Japanese Patent Provisional Publication Nos. 09-073173/1997, 10-010739/1998, 09-230595/1997 and WO97/33198). With respect to F2 laser light (157 nm) which is expected to enable further miniaturization to 0.10 μm or less, difficulty in ensuring transparency increases further, and it has been found that acrylic resins do not permit light transmission therethrough at all and cycloolefin resins having carbonyl bonds have strong absorption. Polymers having a benzene ring have a little improved absorption at a wavelength in the vicinity of 160 nm, which is far-below the practically acceptable level. It has been found that in a monolayer resist, a reduction in carbon-to-carbon double bonds as typified by a benzene ring and carbon-to-oxygen double bonds as typified by a carbonyl group is indispensable for having an adequate light transmittance (International Work Shop 157 nm Lithography MIT-LL Boston, Mass. May 5, 1999). It is reported that introduction of fluorine is effective for improving transmittance (J. Vac. Sci. Technol. B 17(6), November/December 1999). A number of fluorine-containing polymers for resist are proposed (J. Photopolymer Sci. and Techno Vol. 13 No. 4 (2000) p 652-657 and Vol. 13 No. 3 (2000) p 451-458). The transmittance of these polymers, however, does not reach that of polyhydroxystyrene or derivatives thereof adapted for KrF exposure, and poly(meth)acrylic derivatives or polycycloolefin derivatives adapted for ArF exposure.
It is conventionally known that the bilayer resist technique is excellent in the formation of a pattern having a high aspect ratio over a stepped substrate. It is also known that a high-molecular silicone compound having a hydrophilic group such as hydroxy or carboxyl group is necessary for the development of a bilayer resist film in an ordinarily employed alkaline developer.
Proposed is a silicone-type chemically-amplified positive resist material for KrF excimer laser comprising a polyhydroxybenzylsilsesquioxane, which is a stable alkali-soluble silicone polymer having some of the phenolic hydroxyl groups protected with a t-Boc group, and an acid generator (Japanese Patent Provisional Publicatin No. 06-118651/1994, SPIE vol. 1925 (1993) p 377 and others). A positive resist material based on the silsesquioxane obtained by substituting cyclohexylcarboxylic acid with an acid-labile group is proposed for ArF excimer laser (Japanese Patent Provisional Publication Nos. 10-324748/1998, 11-302382/1999 and SPIE vol. 3333-07(1998) p 62). As a resist for F2 laser, proposed is a positive resist material based on the silsesquioxane having hexafluoroisopropanol as a dissolvable group (Japanese Patent Provisional Publication No. 2002-055456).
A silicon-containing (meth)acrylate ester is proposed as a base polymer for resist having silicon as a pendant side chain (Japanese Patent Provisional Publication No. 09-110938/1997 and J. Photopolymer Sci. and Technol. Vo. 9 No. 3(1996) p 435-446).
The silicon-containing polymer of the (meth)acrylate type has a drawback that dry etching resistance thereof with oxygen plasma is weaker than that of a silsesquioxane polymer. This weak dry etching resistance owes to a low silicon content and a difference in the main skeleton of the polymer. The siloxane pendant type of (meth)acrylate also has the drawback that it easily repels a developer and is inferior in wettability with the developer. With a view to overcoming these problems, a trisilane or tetrasilane pendant type of (meth)acrylate-containing polymer having an increased silicon content and an increased alkali dissolution by imparting the silicon-containing group with acid elimination property is proposed (SPIE vol. 3678 p 214, p 241, p 562). Although this polymer shows a strong absorption at a wavelength not greater than 200 nm because of having silicon-silicon bonds, it is used as a polymer having a silicon-containing and acid-eliminating group, which polymer has transparency high enough as a polymer for KrF excimer laser light of 248 nm and is excellent in etching resistance. In addition, the other silicon-containing and acid-labile groups have been investigated (SPIE vol. 3678 p 420).
The term “(meth)acrylic” means methacrylic and/or acrylic.